An understanding of the temperature distribution within the Earth's crust is useful to identify regions of high thermal energy.
In the oil and gas exploration and production industry, the temperature regime in the Earth's crust may determine the reservoir quality and type of hydrocarbons present in a subsurface reservoir and in turn affect the ability to recover hydrocarbons from such a reservoir.
Empirical data presented by Steen and Nadeau (see Steen, Ø., and Nadeau, P. K., 2007, AAPG annual meeting, Long Beach, AAPG Search and Discover Article, #90063) shows that 90% of the world's oil and gas fields are found at a present-day temperature less than 120 centigrades. Hence, it is of great interest to identify this zone. It may similarly be desirable to identify parts of a basin that are likely to be unproductive, have immature source rock, or be gas-prone. The inclusion of temperature in an evaluation of a geological basin is critical for finding sweet spots for oil and gas generation in the basin.
Seismic data may be acquired for imaging the subsurface structure. For example, a seismic survey of a region may be performed in which a seismic wave is transmitted from the surface into the subsurface. Receivers may be then used to measure the amplitude of seismic waves from the subsurface in response to the transmission and the arrival times of the seismic waves relative to the transmission. High amplitude events may be associated with acoustic reflectors in the subsurface rock structure. The data from different lateral locations may be presented in the form of aligned time series traces to form a 2D seismic image of the subsurface showing the time location of different reflectors, time in effect being a proxy for depth. Such an image may reveal the structure of the subsurface. Typically, the amplitudes are plotted against the full two-way travel time (TWT), being the time of a transmitted seismic wave to travel from a seismic source to a subsurface reflector and from the reflector to a seismic receiver. The travel time is dependent upon the seismic velocity of the subsurface rock structure, and may be converted to a true depth amplitude section, for example by employing a “vertical stretch” technique.
The seismic data may be visualised in real time, during acquisition of the data. The acquisition may be performed offshore using a survey vessel. Preliminary processing of the data may be performed. The data may then be transmitted via a communications link to a data room equipped with displays to visualise the data, for example in the form of a 2D seismic image.
Temperature information is often added to seismic images of the seafloor to visualise the temperature distribution. For example, contour maps of TWT projected onto the surface of the seabed may have temperatures overlain, or isotherms may be plotted onto 2D TWT seismic sections.
Current techniques for determining the temperature distribution typically involves using basin modelling software packages, which require geological models in true vertical depth, populated using geophysical properties such as heat conductivity, density, and heat capacity, or use libraries of subsurface lithologies and associated compaction trends. These techniques may compute temperature profiles using a steady state approximation, by solving the equations of Fourier's Law, or solving the full time-dependent heat equation.
Such techniques may not be convenient to use because of the input demands of the software. This may particularly be so in data rooms, where data are accessible or visible to the user for a limited period of time, for example, a couple of hours, or at most two days. In addition, specialist software of this kind may not be available in a data rooms. Furthermore, use of such software may require expert users to operate it.